Trade Secretary Stephen Byers vowed to intervene yesterday, after it emerged that electricity giants are passing new "green" tax bills on to North-East rural post offices.

Mr Byers, MP for North Tyneside, promised to investigate after Vale of York Tory MP Anne McIntosh raised the alarm.

Miss McIntosh told the Commons that Northern Electric and Gas had written to sub-post offices in her constituency telling them they would have to pay the "climate change levy".

The tax aims to encourage companies to reduce energy bills and potentially help avoid global warming, which may have contributed to last month's floods across the North.

She challenged Mr Byers to say whether he was "aware that utility companies, like Northern Electric and Gas, have written to sub-post offices to say that they are passing on the climate change levy to sub-post offices and post offices".

The MP quoted how Mrs Holder, postmistress in the village of Huby, near Easingwold, North Yorkshire had got such a letter.

Miss McIntosh said she was not aware that struggling sub-post offices were "heavy industrial users of electricity.

"Is this not another hammer blow for sub-post offices that will put them out of business in rural areas such as the Vale of York," she asked.

Mr Byers said he was not aware of the individual cases, but vowed to "look with great interest and concern" at the issue raised by Miss McIntosh.

He underlined the Government's commitment to preserving rural post offices by announcing a new scheme to transform post offices into "one stop shops", which can provide access to benefits and health advice.

Northern Electric and Gas confirmed that it was passing on the new levy to commercial customers, including the rural post offices.

However, spokesman Julian Kenyon said: "We are simply passing on a tax that's been imposed by the Government."